NMR in biomedicine
-
The three-dimensional (3D) Look-Locker (LL) acquisition is a widely used fast and efficient T1 mapping method. However, the multi-shot approach of 3D LL acquisition can introduce reconstruction artifacts that result in intensity distortions. Traditional 3D LL acquisition generally utilizes a centric encoding scheme that is limited to a single phase-encoding direction in k space. ⋯ A filtering procedure based on goodness of fit (GOF) is proposed to reduce the effect of false flip angle estimates. Filtering based on GOF weighting can remove probable incorrect angles that result in bad curve fitting. Simulation, phantom and in vivo studies have demonstrated that these techniques can improve the accuracy of 3D LL T1 estimation.
-
Although MRI offers highly diagnostic medical imagery, patient access to this modality worldwide is very limited when compared with X-ray or ultrasound. One reason for this is the expense and complexity of the equipment used to generate the switched magnetic fields necessary for MRI encoding. These field gradients are also responsible for intense acoustic noise and have the potential to induce nerve stimulation. ⋯ Lower field imaging (<1 T) and micro-imaging are favorable application domains as, in both cases, it is technically easier to achieve the short RF pulses desirable for long echo trains, and also to limit RF power deposition. As TRASE is simply an alternative mechanism (and technology) of moving through k space, there are many close analogies between it and conventional B0 -encoded techniques. TRASE is compatible with both B0 gradient encoding and parallel imaging, and so hybrid sequences containing all three spatial encoding approaches are possible.
-
Arterial spin labeling (ASL) has been developed into a useful technique that is capable of quantifying noninvasively local cerebral blood flow (CBF) using the water molecules in arterial blood as diffusible tracers. Pulsed ASL (PASL) is more strongly affected than continuous ASL (CASL) by cardiac pulsation, because the tag bolus is shorter than the cardiac cycle in most cases. No reports have yet clarified the effects of multiple cardiac phases on the quantification of CBF in PASL when triggering is used. ⋯ PPWT-ASL strongly affects CBF values compared with NT-ASL in ACA and MCA territories, especially when measured at the foot of the carotid artery flow phase. CBF_NT was assumed to lie approximately between the minimum and maximum CBFs, with clear statistical significance in several ROIs at several time points of PPWT-ASL, and CBF_NT was assumed to resemble 'randomly triggered' PPWT-ASL. In conclusion, PPWT-ASL strongly affects CBF values compared with NT-ASL, particularly at the foot of the carotid artery flow in ACA and MCA territories.
-
Spectroscopic signals which emanate from complexes between paramagnetic lanthanide (III) ions (e.g. Tm(3+)) and macrocyclic chelates (e.g. 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate, or DOTMA(4-)) are sensitive to physiology (e.g. temperature). Because nonexchanging protons from these lanthanide-based macrocyclic agents have relaxation times on the order of a few milliseconds, rapid data acquisition is possible with chemical shift imaging (CSI). ⋯ Using TmDOTMA(-), we show datasets from a 20 × 20 × 20-mm(3) field of view with voxels of ~1 μL effective volume acquired within 5 min (at 11.7 T) for temperature mapping. By employing reduced spherical encoding with Gaussian weighting (RESEGAW) instead of cubical encoding of k space, a significant increase in CSI signal is obtained. In vitro and in vivo three-dimensional CSI data with TmDOTMA(-), and presumably similar lanthanide-based macrocyclics, suggest that acquisition using RESEGAW can be used for high spatiotemporal resolution molecular mapping with BIRDS.